#cheatsheet #Linux

LinuxCheatSheet.md

Linux CheatSheet

• Check linux version: uname -a, lsb_release -a
• List all open port in a server: nmap localhost
• Change PATH: export PATH=$PATH:/usr/jdk1.7/bin
• Java
  • Javac -cp xxx.jar yyy.java (compile)
  • Java -cp .:xxx.jar yyy (run)
• Open a port: iptables -A FORWARD -p tcp --sport 80 -j ACCEPT
• Check firewall setting: Iptables -L
• Send a mail: mail -s “Hello world” you@youremailid.com [ provided SMTP server is runnin]
• Check if SMTP server is running
  • Telnet 127.0.0.1 25 [checks if SMTP is running is localhost; 25 is default SMTP port]
• Netstat
  • Netstat -tnlp [Lists diff processes running]
• Kill a process: Kill <>
• Remove a directory: rmdir <directory_name> or rm -r [ recursive]
• Check log file: tail -f <xxx.log>
• Unzip a .zip file: unzip .zip
• Search for a specific process: ps -ef|grep jetty
• Delete directory and content recursively: rm -r
• Search for a string in directory/subdirectory recursively
  • Grep -ir "search me" . [ searches recursively starting present directory]
    • i: ignore case
    • r: recursive
• Check size of a directory
  • du -ch [ c: grand total at the end, h : human readable]
  • du -ch|grep total [ gives only the total size of directory/subdirectory]
  • du -sh [ provides summary including size]
• Display installed hard disk and size
  • Fdisk -l|grep '^Disk /dev/'
• Display info about CPU and processing unit: lscpu
• Check amount of used, free and total amount of RAM
  • Free -m
  • Cat /proc/meminfo
• Check the current user: Whoami
• Change to super user: su << for this need to have superuser password>>
• Change to sudo user: sudo -u root –i << for this current user needs to have sudo privilege>>
• Display hidden files in a folder: Ls -a
• Shutdown the system (as root user)
  • Halt
  • Init 0
• Reboot the system (as root user)
  • reboot
  • Init 6
• Change user
  • Su <>
  • Su - [changes to root user, needs root user password]
• List all environment variable: Env
• List all process running (like Task Manager in Windows): Top
• To know wherefrom a particular command is run: Which <> [eg: which mvn/ls/npm]
• History of commands are stored in /home/de393369/.bash_history
• To know details of some command: Man <> [ eg man cat]
• Check user details: Finger <>
• Check user id, group id of an user: Id <>
• Important files
  • /etc/passwd - user details like userid, group id etc
  • /etc/shadow - user password details
  • /etc/login.def - has defaults like uid min/max, password size etc.
  • /etc/skel/* - files that will be copied to home dir when new user is added
  • /etc/group - has group details
  • /etc/sysconfig/network-scripts - has details of network card
• Utility to check errors in password file
  • Pwck
  • Pwconv
• Get list of users logged in a server: W
• Who command: Who -b [ last boot time], Who -q [ show how many users are there]
• Check what an user has logged in last: Last <>
• Adding a user: Useradd <> [gets default setting from /etc/default/useradd]
• Remove a user: Userdel -r <> [ deletes user and home directory]
• Download from network/internet: wget
• Untar a .gz file: tar -xzf hadoop-1.2.1.tar.gz
• Remove a file from a WAR file
  • zip -d MCE.war WEB-INF/lib/axis.jar [ removes axis.jar from MCE.war]
  • zip -d MCE.war WEB-INF/lib/cxf*.jar [ removes all jars starting with cxf from MCE.war]
• Add a file to a WAR file: zip -ur MCE.war WEB-INF/lib/axis.jar [ adds axis.jar to MCE.war]
• Rename a file: mv oldfile newfile
• Find string in specific files in directory: find . -name "module.xml"|xargs grep -i "org.springframework.spring"
• List content of a jar file: jar -tvf
• Vim command [ http://www.worldtimzone.com/res/vi.html]
  • Shft + G [ end of file]
  • :0 [move to the start of the file]
  • Cntl + U [ 1 page up]
  • Cntl + d [ 1 page down]
  • Highlight text in Vi editor to copy to windows clipboard
  • /xxxx [ search for a pattern; case sensitive]
• #!/bin/ksh
  • 1st line in shell script
  • Tells the OS that ksh interpreter is to be used to run the script
• Return to home directory: *cd ~*
• Getting help: * --help *
• Run a shell script: Bash XXXXX.sh
• List of processes listening upon a port: Netstat -tulpn
• Get IP address: ifconfig
• Set environment variables
  • Set variables(eg. JAVA_HOME) in .bash_profile

    export JAVA_HOME=/usr/java/jdk1.8.0_91
    PATH=$PATH:$JAVA_HOME/bin
    export PATH
    

  • Run "source ~/.bash_profile"
• Download from internet: wget [url]
• Extract file from archive: tar xvf file.tar
• Create a tar archive of all *.c file in current directory: tar cvf file.tar *.c

MacOS

• List of all processes: netstat -vanp tcp
• Find process using a port (e.g. 3000)
  • netstat -vanp tcp | grep 3000
  • lsof -i tcp:3000